We anticipate using our established ranges of variability of the simultaneous displacement patterns of normal walking to serve as baselines for comparing the gait patterns of patients with selected neurological, skeletal or arthritic disabilities. We plan to characterize selected gait abnormalities and to assess the changes in performance after major surgical or medical treatment procedures. This year we will be studying primarily total joint replacements. The nature and amount of force applied to canes and crutches will be monitored simultaneously with the kinematic records. We also plan to study mechanisms which are operable in causing the gait abnormalities of the patients, such as muscle weakness, joint immobility, postural unsteadiness and instability, and muscle spasticity or rigidity. Bibliographic references: Murray, M.P., Brewer, B.J., Gore, D.R. and Zuege, R.C.: Kinesiology after McKee-Farrar Total Hip Replacement: A Two-Year Follow-up of 100 Cases. J. Bone Joint Surg. 57-A: 337-342, April 1975. Murray, M.P., Seireg, A. A. and Sepic, S.B.: Normal Postural Stability and Steadiness: Quantitative Assessment. J. Bone Joint Surg. 57-A: 510-516, June 1975.